Projection screens



. March 31, 1964 J. HOURDIAUX 3,126,783

PROJECTION SCREENS, IN PARTICULAR FOR MOVING PICTURES Filed Dec. 14, 1961 2 Sheets-Sheet 1 March 31, 1964 J. HOURDIAUX 3,126,788

PROJECTION SCREENS, IN PARTICULAR FOR MOVING PICTURES Filed Dec. 14, 1961 2 Sheets-Sheet 2 United States Patent 3,126,788 PROJECTION SCREENS, IN PARTICULAR FOR MOVING PICTURES Jules Hourdiaux, 96 Ave. de Versailles, Paris, France Filed Dec. 14, 1961, Ser. No. 159,311 Claims priority, application France Dec. 22, 1960 2 Claims. (Cl. 88--28.9)

The present invention relates to projection screens consisting of a juxtaposition of elongated rectilinear elements and in particular screens for the projection of moving pictures thereon.

The object of this invention is to provide a screen of this kind of which may be shaped to have a projection surface either concave or convex without the picture projected on the screen being deformed or without dark zones being visible to the spectators whatever be their position with respect to the screen.

With this object in view, according to my invention each of these elements of the screen comprises, on the one hand, means for guiding two elements identical to that considered and adjoining it on opposite sides thereof, so that said two elements are pivotable with respect to said first mentioned element about two respective axes parallel to said direction and fixed with respect to said first mentioned element and, on the other hand, a convex cylindrical projection surface having generatrices parallel to said direction and the limit generatrices of which are located in a plane making, with the plane passing through said axes, an angle ranging from to 30 and, preferably, from to Preferred embodiments of my present invention will be hereinafter described with reference to the accompanying drawings, given merely by way of example and in which:

FIG. 1 is a cross sectional view of an element of a screen made according to a first embodiment of my invention.

FIG. 2 is a view similar to FIG. 1, relating to another embodiment of this invention.

FIG. 3 is a perspective view of a concave screen made according to my invention.

FIG. 4 is a plan view of a convex screen made according to my invention.

Each of the elements of a screen, designated by reference numeral 1 (FIGS. 1, 3 and 4) or 1,, (FIG. 2), comprises, on the one hand, guiding means allowing two identical elements held on opposite sides of the element that is considered and in contact therewith, to pivot about two longitudinal axes fixed with respect to said element (these axes being projected in FIGS. 1 and 2, at points 0,, and 0,, respectively), and on the other hand, a convex cylindrical projection surface C the limit generatrices of which (which are projected at points E and F, FIGS. 1 and 2) parallel to said axes, define a plane P which makes with the plane Q passing through axes O, and 0,, an angle I ranging from 15 to or preferably from 20 to 25 In the construction of FIG. 1, the elements are of cylindrical shape, the term cylinder designating the surface generated by a straight line that remains parallel to a given direction and which glides along a curve called directrix.

In the construction of FIG. 1, this directrix comprises two circular arcs a and b which may be approximately deduced from each other by translatory displacement parallel to the line X-X passing through their centers, located on O and 0 respectively, these circular arcs therefore having the same radius r. These circular arcs define two cylindrical surfaces A and B (FIGS. 3 and 4) one of which is convex and the other concave, these two ice cylindrical surfaces forming the above mentioned guiding means.

The directrix further comprises, on the other hand, a curve 0 (FIG. 1) more or less of the form of a circular arc joined tangentially to said circular are a corresponding to the convex guiding surface A, the chord of curve 0 being shown at HP. This curve 0 is the directrix of the convex surface C (FIGS. 3 and 4). As shown by the drawings, line EF intersects line X-X at a point located on the other side of center 0,, from center O The maximum distance between curve c and line F, is equal to about A of the distance d between centers 0 and O Advantageously, this curve c is a circular arc, the radius R of which is about 20'. The radius 0,,F which separates circular arc a from curve 0 makes with straight line X--X an angle J ranging from 35 to 55.

Curve 0 is joined to circular arc b by a line such that if a second identical element is mounted adjacent to the first one, with its convex guiding surface A applied against the concave guiding surface B of the element that is being considered, the surface C of the second element does not come into contact with any point of the element that is considered.

For this purpose, according to the construction of FIG. 1, curve 0 is joined to circular arc b by a rectilinear line I and a circular are m having the same radius as circular are c and the center of which is chosen in such manner that circular are n is joined tangentially to circular arc b.

Elements 1 are kept in place with one another along their respective guiding surfaces A and B, by means of several cables 2 (FIGS. 3 and 4) passing through holes 3 (FIG. 1) substantially parallel to the line X-X and located at different places along the height of elements 1. These cables may have a nondeformable cross section, being for this purpose made of metal, in which case they have a diameter substantially equal to one half of the diameter of holes 3 to permit relative displacements of elements 1, or they may have a deformable cross section, being made for instance of rubber, either natural or synthetic, and in this case their flexibility may be sufiicient to permit relative displacement of elements 1 with respect to one another.

In the modification of FIG. 2, the concave guiding surfaces b are provided only from place to place on projections 4 of this element, at least some of these projections having the holes 3 formed therein. In this case, outside of the places where projections are provided, element It: may be of a practically uniform thickness, the directrix of the cylindrical surface comprising a rectilinear portion l analogous of that of FIG. 1 and a curve n parallel to curve c.

Whatever be the embodiment that is chosen, the width of elements 1 or 1a must be chosen in accordance with the dimensions of the projection room, this width being the smaller as the radius of the curvature of the screen and the distance from this screen to the first row of spectators are themselves smaller.

I thus obtain a screen which may be given any designed shape either convex or concave as illustrated by FIGS. 3 and 4, where the general direction of travel of the light rays is indicated by an arrow. I may provide two central elements facing each other by their concave guiding surfaces (FIG. 3) or by their convex guiding surfaces (FIG. 4), the respective elements 1 being disposed vertically, i.e. parallelly to the small side of the projected picture.

Owing to the above described guiding means, it is possible to rotate, through a limited angle, the elements with respect to one another so as to give the screen the desired shape, either curvilinear or polygonal or again consisting of a combination of curves and straight lines. Furthermore, owing to the inclination of the elementary projection surfaces C at angle I, the direction of these surfaces does not vary very much with respect to the direction of the light rays. The shadows formed by every element upon the next one are extremely fine and for practical purposes are not visible. Finally, the horizontal deformation of the picture from the center toward the sides is little perceptible, as demonstrated experimentally.

In a general manner, while I have, in the above description, disclosed what Ideem to be practical and efficient embodiments of my invention, it should be well understood that I do not wish to be limited thereto as there might be changes made in the arrangement, disposition and form of the parts without departing from the principle of the present invention as comprehended within the scope of the accompanying claims.

What I claim is:

l. A projection screen comprising a multiplicity of identical elongated elements extending all in the same direction and juxtaposed to oneanother, each of said elements comprising a convex and a concave cylindrical surface for guiding two elements adjoining the element considered on opposite sides thereof so that said two elements are pivotable with respect to said first mentioned element about two respective axes parallel to said direction and fixed with respect to said first mentioned element, said convex and concave surfaces having their generatrices parallel to said direction and having as respective directrices two circular arcs of the same radius, said circular arcs having their respective centers located on said axes and a convex cylindrical projection surface joined tangentially with said convex surface, saidprojection surface having generatrices parallel to said direction and the limit generatrices of which are located in a plane making, with the plane passing through said axes, an angle ranging from 15 to 30.

2. A projection screen according to claim 1 wherein the maximum distance between said cylindrical projection surface and the plane passing through the two limit generatrices thereof is approximately one-tenth of the distance between said axes.

References Cited in the file of this patent UNITED STATES PATENTS 1,550,197 Berry Aug. 18, 1925 FOREIGN PATENTS 894,186 France Dec. 15, 1944 

1. A PROJECTION SCREEN COMPRISING A MULTIPLICITY OF IDENTICAL ELONGATED ELEMENTS EXTENDING ALL IN THE SAME DIRECTION AND JUXTAPOSED TO ONE ANOTHER, EACH OF SAID ELEMENTS COMPRISING A CONVEX AND A CONCAVE CYLINDRICAL SURFACE FOR GUIDING TWO ELEMENTS ADJOINING THE ELEMENT CONSIDERED ON OPPOSITE SIDES THEREOF SO THAT SAID TWO ELEMENTS ARE PIVOTABLE WITH RESPECT TO SAID FIRST MENTIONED ELEMENT ABOUT TWO RESPECTIVE AXES PARALLEL TO SAID DIRECTION AND FIXED WITH RESPECT TO SAID FIRST MENTIONED ELEMENT, SAID CONVEX AND CONCAVE SURFACES HAVING THEIR GENERATRICES PARALLEL TO SAID DIRECTION AND HAVING AS RESPECTIVE DIRECTRICES TWO CIRCULAR ARCS OF THE SAME RADIUS, SAID CIRCULAR ARCS HAVING THEIR RESPECTIVE CENTERS LOCATED ON SAID AXES AND A CONVEX CYLINDRICAL PROJECTION SURFACE JOINED TANGENTIALLY WITH SAID CONVEX SURFACE, SAID PROJECTION SURFACE HAVING GENERATRICES PARALLEL TO SAID DIRECTION AND THE LIMIT GENERATRICES OF WHICH ARE LOCATED IN A PLANE MAKING, WITH THE PLANE PASSING THROUGH SAID AXES, AN ANGLE RANGING FROM 15 TO 30*. 